This application is based on Application No. 2002-002322, filed in Japan on Jan. 9, 2002, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a fuel supply device for an internal combustion engine, and more particularly to a fuel supply device for an internal combustion engine, which supplies fuel while controlling the pressure of the fuel supplied to the internal combustion engine.
2. Description of the Related Art
An example of a conventional fuel supply device for an internal combustion engine is disclosed in Japanese Patent Application Laid-open No. 11-324757. In this fuel supply device, a target fuel pressure and the detected fuel pressure are used to set a feedback quantity, and the pump discharge quantity which corresponds to the target fuel pressure change amount, and the fuel quantity that is supplied to the engine by a fuel injection valve, are set as a feed forward quantity.
Explanation will now be made of the construction and operation of the conventional fuel supply device, using FIG. 1. A feed pump 102 draws fuel up from a fuel tank 101. Fuel which has passed through a filter 103 is pressure-regulated by a regulator 104 and introduced into a high-pressure pump 105. A piston 107 moves up and down by means of a pump cam 112, which rotates as a single unit with a cam shaft for an air intake or exhaust valve. As a result, the volume of a pressure chamber 118 changes, and the pressurized fuel is introduced into a fuel rail 113. The quantity of fuel introduced into the fuel rail 113 is adjusted by means of a spill valve 108.
Electricity passing through a coil 110 causes the spill valve 108 to rise and overcomes a spring 111, thereby opening a valve 109. When the valve 109 opens, the pressure chamber 118 is communicated to the fuel intake side. Thus, the fuel returns to the fuel intake side without being sent to the fuel rail 113. Therefore, the fuel is not discharged from the pump to the fuel rail 113.
When fuel pressure inside the fuel rail 113 reaches the valve-opening pressure for a relief valve 114, the relief valve 114 opens, and the fuel in the fuel rail 113 returns to the fuel tank 101. A fuel pressure sensor 116 detects the fuel pressure inside the fuel rail 113, and sends this to an ECU 117, which thus performs feedback control and the like. The injector 115 directly supplies the pressurized fuel in the fuel rail 113 to the combustion chamber inside the internal combustion engine.
FIG. 2 shows the relationship between the pump cam 112 and a drive signal sent to the spill valve 108. Note that the rotation angle of the pump cam 112 is measured by means of a cam sensor 120 shown in FIG. 1. In FIG. 2, reference numeral 10 indicates how the diameter of the pump cam 112 changes in relation to the piston 107, and reference numeral 11 indicates changes in the drive signal. As shown in FIG. 2, when the pump cam 112 is ascendant, the piston 107 moves upward and thus the volume of the pressure chamber 118 decreases, whereby the fuel is compressed. In the case where the spill valve 108 driving signal is ON, the fuel is returned to the fuel intake side. Therefore, fuel is not discharged to the fuel rail 113. Even during the fuel discharge stroke, the spill valve 108 is closed only in the case where the drive signal to the spill valve 108 is OFF. Therefore, the discharge of the fuel to the fuel rail 113 side is effective. By controlling the spill valve ON/OFF periods, the effective pump discharge quantity is controlled to thereby control the fuel pressure.
The appropriate fuel pressure depends on the operating state of the engine. Typically, the fuel pressure varies within a range of approximately 3-12 Mpa. Depending on the fuel rail volume, for example, approximately 100 mcc of fuel is necessary to cause the fuel pressure to increase by 1 Mpa. In order to cause the fuel pressure to change by 9 Mpa, approximately 900 mcc of fuel must be introduced into the fuel rail. On the other hand, one pump cycle by a high-pressure pump can only pump out approximately 100 mcc of fuel at maximum. As such, in the case where the target fuel pressure is changed by a large amount, it is necessary to continue the maximum discharge over several cycles, in which the fuel which needed to be pumped out but could not be pumped out in one cycle is pumped out in the next cycle.
FIG. 10 explains control operations in the conventional fuel supply device shown in FIG. 1. In FIG. 10, the computed target fuel pressure, which varies with each engine operating state, is read at reference numeral 1001. At reference numeral 1002, the target fuel pressure from the previous cycle is computed. The difference between the target fuel pressure computed at reference numeral 1001 and the previous cycle target fuel pressure computed at 1002 is computed at reference numeral 1003 as a target fuel pressure difference. Next, at reference numeral 1004, the pump discharge quantity is computed from the target fuel pressure difference, using a predetermined correspondence map which is prepared in advance. At reference numeral 1005, a carry over quantity 1016 from the previous cycle, which will be described later, is added to the pump discharge quantity to compute the feed forward quantity. At reference numeral 1007, an injector injection quantity 1006, the feed forward quantity and a feedback correction quantity are added together to produce a total pump discharge quantity 1008. Here, the feedback quantity refers to a quantity computed at reference numeral 1014 by adding together a proportional gain 1010 and integral amounts which are given based on the difference between the target fuel pressure 1001 and actual fuel pressure 1008. Next, at reference numeral 1015, a pump one discharge quantity is computed from the total pump discharge quantity. At reference numeral 1018, the pump one discharge quantity is converted into a spill valve control angle 1019. Note that at reference numeral 1017 the pump one discharge quantity is subtracted from the total pump discharge quantity, and the remainder becomes the carry over quantity 1016 for the next cycle.
Explanation will now be made of the operations, using the flow chart shown in FIG. 9. The target fuel pressure (FPt), which varies depending on the engine operating state, is computed at step S801. At step S802, the target fuel pressure difference (DPt) is computed based on the target fuel pressure (FPt) and the previous cycle target fuel pressure (FPt[ixe2x88x921]). At step S803, the correspondence map is used to produce a target fuel pressure differential flow rate (Qt) from the target fuel pressure difference (DPt), for example. At step S804, the target fuel pressure differential flow rate (Qt) and the previous cycle""s carry over quantity (Qcarry[ixe2x88x921]) are added together to produce the feed forward quantity (Qff). At step S806, the feedback correction quantity (Qfb) is computed from the difference between the target fuel pressure (FPt) and the actual fuel pressure (FPd). At step S807, the feed forward quantity (Qff), the injection quantity (Qinj) and the feedback correction quantity (Qfb) are added together to computed the total pump discharge quantity (Qall). At step S808, the pump one discharge quantity (Qone) is computed on the basis of the total pump discharge quantity by setting a limit value therefor. At step S809, the pump one discharge quantity (Qone) is subtracted from the total pump discharge quantity (Qall) to produce the carry over quantity for the next cycle (Qcarry). The next cycle carry over quantity becomes the previous cycle carry over quantity (Qcarry[ixe2x88x921]) when this computation process is performed in the next cycle. At step S810, the spill valve control angle is computed from the pump one discharge quantity to control the ON/OFF angle of the spill valve, whereby it is possible to control the pump discharge quantity and the fuel pressure.
In the conventional device described above, the feedback control is executed even though the feed forward control is being executed. Therefore, the feedback control is executed based on the difference between the target fuel pressure and the actual fuel pressure, while in a state where the feed forward control is being executed and the actual fuel pressure has not caught up with the target fuel pressure. Therefore, there was a problem that the feedback correction quantity deviates from a correct value, and further, when the feed forward control ends, the deviation of the feedback correction amount causes the actual fuel pressure to deviate from the target fuel pressure, thus generating an overshoot when the target fuel pressure is raised and an undershoot when the target fuel pressure is lowered.
The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a fuel supply device for an internal combustion engine, which is capable of preventing fuel pressure control problems caused by divergence of a feedback correction quantity in the pump control.
The present invention relates to a fuel supply device for an internal combustion engine, which includes: target fuel pressure computing means for computing a target fuel pressure based on an operating state of the internal combustion engine; fuel pressure detecting means for detecting actual fuel pressure; injector injection quantity computing means for computing an injection quantity by an injector; feed forward quantity computing means for computing as a feed forward quantity a pump discharge quantity calculated in accordance with an amount of change in the target fuel pressure that is computed by the target fuel pressure computing means; feedback correction quantity computing means for computing a feedback correction quantity based on the target fuel pressure and on the actual fuel pressure detected by the fuel pressure detecting means; and fuel pressure controlling means for controlling fuel pressure by controlling an angle of a spill valve based on the feed forward quantity, the injector injection quantity and the feed back correction quantity. In this fuel supply device, the computation of the feedback correction quantity by the feedback correction quantity computing means is stopped when the feed forward quantity is not within a given range. As such, the feedback control is stopped while the feed forward quantity (Qff) is not in the given range, which is to say it is stopped while the feed forward control is being performed. Therefore, it becomes possible to suppress undershooting/overshooting of the target fuel pressure by the actual fuel pressure following completion of the feed forward control.